Lyme disease is a vector-borne infectious disease caused by Borrelia burgdorferi, transmitted by ticks of genus Ixodes. Its most common manifestation is a rash, but it can cause debilitating, chronic neurologic and fatigue syndrome. Once the disease is established, long-term antibiotic treatment may be needed.
According to the Centers for Disease Control, Lyme disease is diagnosed based on symptoms, objective physical findings (such as erythema migrans, facial palsy, or arthritis), and a history of possible exposure to infected ticks. Laboratory testing is useful when the characteristic rash is not present. Nevertheless, clinicians should remember that not all patients have the classic rash, and other diseases can produce similar skin symptoms.
The true incidence of the rash, erythema migrans, is disputed, with estimates ranging from less than 50% to over 80% of those infected. A systematic review by the Rational Clinical Examination of studies estimates that 80% of patients may have an expanding rash, erythema migrans (EM), at the site of the tick bite. Most patients with EM do not recall a deer tick bite.
The Rational Clinical Examination review found that the characteristic "bull's-eye" rash with central clearing is present in about 20% of endemic cases in the United States; whereas in Europe and the non-endemic United States 80% of rashes have central clearing.In endemic areas of the United States homogeneously red rashes are more frequent. The rash is classically 5 to 6.8 cm in diameter appearing as an annular homogenous erythema (59%), central erythema (30%), central clearing (9%), or central purpura (2%).
Sometimes, erythema migrans may be less than 5 cm in diameter. Multiple painless EM rashes may occur, indicating disseminated infection.
Neurologic symptoms (neuroborreliosis) may occur in 18%. Bannwarth's syndrome is the triad of lymphocytic meningitis, cranial nerve palsy, and radiculoneuritis. The most common cranial palsy is the 7th cranial nerve (facial paralysis) in the form of Bell's Palsy.
If the diagnosis cannot be made clinically, the Centers for Disease Control recommend a two-step immunologic process when testing blood for evidence of Lyme disease. Both steps can be done using the same blood sample.
- The first step uses an ELISA or IFA test. These tests are designed to be very "sensitive," meaning that almost everyone with Lyme disease, and some people who don't have Lyme disease, will test positive. If the ELISA or IFA is negative, it is highly unlikely that the person has Lyme disease, and no further testing is recommended. If the ELISA or IFA is positive or indeterminate (sometimes called "equivocal"), a second step should be performed to confirm the results.
- The second step uses a Western blot test. Used appropriately, this test is designed to be "specific," meaning that it will usually be positive only if a person has been truly infected. If the Western blot is negative, it suggests that the first test was a false positive, which can occur for several reasons. Sometimes two types of Western blot are performed, "IgM" and "IgG." Patients who are positive by IgM but not IgG should have the test repeated a few weeks later if they remain ill. If they are still positive only by IgM and have been ill longer than one month, this is likely a false positive.
CDC does not recommend testing blood by Western blot without first testing it by ELISA or IFA. Doing so increases the potential for false positive results. Such results may lead to patients being treated for Lyme disease when they don't have it and not getting appropriate treatment for the true cause of their illness.
In general, CDC does not recommend other tests, the accuracy and utility of which have not been established. They include urine antigen tests, immunofluorescent staining for cell wall-deficient forms of Borrelia burgdorferi, and lymphocyte transformation tests. .
Chronic Lyme disease controversy
There is extensive discussion over whether Lyme disease can be a chronic disease.
The same Ixodes tick carries a parasitic infection, babesiosis. While the distribution of this parasite is not as great as of B. burdorferi, in certain geographic areas, it has been estimated that up to 20% of ticks may carry both diseases.
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